Ducted rotor



1964 R. K. WERNICKE 3,117,716

DUCTED ROTOR Filed April 10, 1963 INVENTOR. RODNEY K- WEP/V/CK! AT TOPNE Y5 v United States Patent 3,117,716 DUCTED ROTOR Rodney K. Wernicke,Hurst, Tern, assignor to Bell Aerospace Corporation, Wheatfield, N.Y.Filed Apr. 10, 1963, Ser. No. 272,141 7 Claims. ((31. 230-120) Thisinvention relates to ducted propellers, fans, or the like; and moreparticularly to means for improving the efiiciency of operation thereof.

Whereas it is well known that for maximum efficiency a ducted propelleror fan or the like must operate with minimum blade tip clearancerelative to its shroud, due to inequalities of manufacture and typicalhazards of usage it has heretofore been requisite to provide anundesirably large gap between the blade tip path and the wall of theenclosing duct in order to insure against accidental collision and/orundesirable frictional contact therebetween.

It is an object of the present invention to provide an improved form ofblade for propellers or fans or other rotor arrangements when used inducted systems, whereby the blade may operate with safety substantiallycloser to the duct Wall, compared to prior ducted rotor arrangements.

Another object is to provide an improved device as aforesaid an improvedrotor blade tip construction whereby the blade tip path automaticallyadjusts relative to the duct wall to provide minimum clearancetherebetween. Another object is to provide an improved bladeconstruction including a floating blade tip shoe which automaticallymoves into close-fitting relation with the enveloping duct, while at thesame time rictional contacts therebetween are precluded.

Other objects and advantages of the invention will appear from thespecification hereinafter and in the accompanying drawings, wherein:

FIG. 1 is a fragmentary plan view of a rotor blade and an associatedduct or cowling, embodying the features of the present invention;

FIG. 2 is a fragmentary front edge view of the device in FIG. 1;

FIG. 3 is an enlarged scale plan view corresponding to a portion of FIG.1, but showing a modified arrangement of the invention;

FIG. 4 is a fragmentary front edge view of the device of FIG. 3; and

FIG. 5 is an end view of the rotor blade tip arrangement of FIGS. 3, 4.

FIGS. 1-2 illustrate an embodiment of the invention in connection with aducted rotor system including a cylindrical duct Within which isrotating a rotor blade designated generally at 12 and arranged to bedriven as by means of a rotor shaft 14. The direction of rotation of theblade 12 is indicated by the arrow in FIG. 1. In accord with the presentinvention the blade tip and portion is hollowed as indicated at 16 toreceive in telescopic fitting relation therein a shoe 18 which isgenerally profiled at its end face to complement the curvature of thecowling 10. In one form of the invention however, as shown in FIGS. l2,the end face 20 of the shoe 18 is curved adjacent its leading edge on asharper radius than the curve of the cowling 10, so that the leading endportion of the shoe is disposed further away from the cowling 10 thanare the main body portions of the shoe. Thus, as the blade swings insidethe cowling 10 a quantity of air will be entrapped by the funnel-shapedopening formed between the leading end of the shoe 18 and the cowling10, and is compressed into the form of an air film upon which the shoerides as the blade rotates, instead of sliding against the cowling 10.

It will of course be understood that centrifugal forces,

"ice

due to rotation of the blade, will automatically bias the shoe 18outwardly toward the cowling; but, as explained hereinabove, the film ofair entrapped between the shoe and the cowling will preclude any actualcontact therebetween. As shown in FIG. 2, the end face of the shoe 18 atthe leading edge thereof may be concave-shaped, as indicated at 22; toenhance the entrapment of air between the shoe and the cowling wall forthe purpose explained hereinabove.

FIGS. 35 illustrate a modified form of blade shoe arrangement wherein atension spring as indicated at 25 is provided to assist the film ofentrapped air to maintain the shoe in minutely spaced relation from thecowl surface, against the action of centrifugal forces imposed upon theshoe as the blade rotates. In addition, the spring acts to retract theshoe into the blade when the blade is not rotating. FIGS. 3-5 alsoillustrate other arrangements for mounting the shoe on the blade and forcreating the desired air cushion bet een the cowling wall and the bladeshoe. Thus, in this case the shoe is illustrated to be of open end form,and mounted and guided to float relative to the main blade structure bymeans of pins 28, 30 slidably fitting telescopically in openings formedin the blade structure.

In lieu of forming the leading edge of the blade shoe in funnel-likemanner to entrap air as shown in FIGS. 3-5, a ram air inlet opening 26may be provided in the leading edge of the blade to extend inwardlytherefrom and then into communication with a spanwise directed channel32. The opening for the mounting pin 28 and the air inlet channel 32 maybe coincident; for example, the mounting pin 28 may be hollowed toconvey the ram air, or a totally separate opening may be employed aspreferred. in any case the ram air is thus directed to flow into theinterior of the shoe 13 by reason of the air ram and/or centrifugalpumping action, to form a cushion of compressed air between the shoe andthe duct wall 14), thereby permitting the overall blade tip structure tofollow a path of minimum clearance with the shroud as explainedhereinabove.

The blade tip extension or shoe member is preferably formed of somelightweight material such as Teflon or some other suitable plasticmaterial having a low coefficient of friction, because during periodswhen the propeller is not running at full speed there may be temporarysurface contacts between the shoe and the shroud.

It will of course be appreciated that whereas only a few forms of theinvention have been illustrated and described in detail by way ofexample herein, various changes may be made therein without departingfrom the spirit of the invention or the scope of the following claims.

I claim:

1. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

a fan blade rotatably mounted concentrically within said shroud andhaving an end portion terminating closely adjacent to but spaced fromthe inner surface of said shroud,

said end portion of the blade having a recess therein opening towardsaid inner surface of the shroud,

a shoe device slidably received in said recess for movement beyond saidend portion of the blade toward contact with the inner surface of saidshrorud under the influence o-f centrifugal force effected by rotationof said blade,

means for rotating said blade in a predetermined direction,

said shoe having an arcuate outer end face of substantially the sameradius of curvature as the inner surface of said shroud,

and means for forming a cushion of air bet-ween said shoe and said innersurface of the shroud to maintain 6 said shoe out of contact with suchinner surface of the shroud,

said means comprising a leading edge outer end face of said shoe whichis of lesser radius of curvature than said inner surface of the shroud.

2. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

a fan blade rotatably mounted concentrically within said shroud andhaving an end portion terminating closely adjacent to but spaced fromthe inner surface of said shroud,

said end portion of the blade having a recess therein opening towardsaid inner surface of the shroud,

a shoe device slidably received in said recess for movement beyond saidend portion of the blade toward contact with the inner surface of saidshroud under the influence of centrifugal force effected by rotation ofsaid blade,

means for rotating said blade,

said shoe having an arcuate outer end face of substantially the sameradius of curvature as the inner surface of said shroud,

means for forming a cushion of air between said shoe and said innersurface of the shroud to maintain said shoe out of contact with suchinner surface of the shroud,

and means for mounting said shoe within said blade and resilientlyresisting outward movement of said shoe.

3. The assembly as defined in claim 2, wherein said shoe is hollow andprovided with an opening at said outer end face thereof,

said means for forming a cushion of air comprising duct means extendingfrom the leading edge of said blade into the hollow interior of saidshoe.

4. The assembly as defined in claim 3, wherein said duct means includesa guide pin carried by said shoe and extending radially inwardlytherefrom into telescoping relation with said blade.

5. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

a fan blade rotatably mounted concentrically within said shroud andhaving an end portion terminating closely adjacent to but spaced fromthe inner surface of said shroud,

said end portion of the blade having a recess therein opening towardsaid inner surface of the shroud,

a shoe device slidably received in said recess for movement beyond saidend portion of the blade toward contact with the inner surface of saidshroud under the influence of centrifugal force effected by rotation ofsaid blade,

means for rotating said blade,

said shoe having an arcuate outer end face of substantially the sameradius of curvature as the inner surface of said shroud and beingrecessed inwardly from said outer end face to provide a pocket opposedto said inner face of the shroud,

and duct means extending from the leading edge of said blade to saidpocket to build up a cushion of superatmospheric air therein to maintainsaid shoe out of contact with the inner surface of said shroud.

6. The assembly as defined in claim 5 wherein said duct means includes ahollow guide pin projecting radially inwardly from said shoe andtelescopically, slidably received in said blade.

7. A-ducted fan assembly comprising, in combination,

a cylindrical shroud,

a fan blade rotatably mounted concentrically within said shroud andhaving an end portion terminating closely adjacent to but spaced fromthe inner surface of said shroud,

said end portion of the blade having a recess therein opening towardsaid inner surface of the shroud,

a shoe device slidably received in said recess for movement beyond saidend portion of the blade toward contact with the inner surface of saidshroud under the influence of centrifugal force effected by rotation ofsaid blade,

means for rotating said blade so as to urge said shoe radially outwardlytoward said inner surface of said shroud,

and said shoe including means cooperative with said inner surface ofsaid shroud for building up and maintaining a cushioning film of airbetween said shoe and such inner surface of the shroud.

References Cited in the file of this patent UNITED STATES PATENTS625,182 Mason May 16, 1899 2,776,107 Willi Jan. 1, 1957 2,814,512 Quinnet al Nov. 26, 1957 2,857,150 Sharp Oct. 21, 1958 FOREIGN PATENTS389,793 Germany Feb. 7, 1924 446,821 France Oct. 11, 1912

1. A DUCTED FAN ASSEMBLY COMPRISING, IN COMBINATION, A CYLINDRICALSHROUD, A FAN BLADE ROTABLY MOUNTED CONCENTRICALLY WITHIN SAID SHROUDAND HAVING AN END PORTION TERMINATING CLOSELY ADJACENT TO BUT SPACEDFROM THE INNER SURFACE OF SAID SHROUD, SAID END PORTION OF THE BLADEHAVING A RECESS THEREIN OPENING TOWARD SAID INNER SURFACE OF THE SHROUD,A SHOE DEVICE SLIDABLY RECEIVED IN SAID RECESS FOR MOVEMENT BEYOND SAIDEND PORTION OF THE BLADE TOWARD CONTACT WITH THE INNER SURFACE OF SAIDSHROUD UNDER THE INFLUENCE OF CENTRIFUGAL FORCE EFFECTED BY ROTATION OFSAID BLADE, MEANS FOR ROTATING SAID BLADE IN A PREDETERMINED DIRECTION,SAID SHOE HAVING AN ARCUATE OUTER END FACE OF SUBSTANTIALLY THE SAMERADIUS OF CURVATURE AS THE INNER SUREFACE OF SAID SHROUD, AND MEANS FORFORMING A CUSHION OF AIR BETWEEN SAID SHOE AND SAID INNER SURFACE OF THESHROUD TO MAINTAIN SAID SHOE OUT OF CONTACT WITH SUCH INNER SURFACE OFTHE SHROUD, SAID MEANS COMPRISING A LEADING EDGE OUTER END FACE OF SAIDSHOE WHICH IS OF LESSER RADIUS OF CURVATURE THAN SAID INNER SURFACE OFTHE SHROUD.